On 11/29/16 1:36 AM, Chandan Rajendra wrote: > When executing btrfs/126 test on kdave/for-next branch on a ppc64 guest, I > noticed the following call trace. > > [ 77.335887] ------------[ cut here ]------------ > [ 77.336115] WARNING: CPU: 0 PID: 8325 at > /root/repos/linux/fs/btrfs/qgroup.c:2443 > .btrfs_qgroup_free_refroot+0x188/0x220 > [ 77.336303] Modules linked in: > [ 77.336393] CPU: 0 PID: 8325 Comm: umount Not tainted > 4.9.0-rc5-00062-g6b74e43 #22 > [ 77.336526] task: c00000062b8d4880 task.stack: c00000062b9a4000 > [ 77.336638] NIP: c0000000005cf018 LR: c0000000005ceff8 CTR: > c0000000005390c0 > [ 77.336771] REGS: c00000062b9a7450 TRAP: 0700 Not tainted > (4.9.0-rc5-00062-g6b74e43) > [ 77.336908] MSR: 800000000282b032 > [ 77.336960] < > [ 77.337027] SF > [ 77.337053] ,VEC > [ 77.337087] ,VSX > [ 77.337114] ,EE > [ 77.337146] ,FP > [ 77.337173] ,ME > [ 77.337207] ,IR > [ 77.337233] ,DR > [ 77.337267] ,RI > [ 77.337294] > > [ 77.337330] CR: 88000842 XER: 00000000 > [ 77.337392] CFAR: c0000000005c9b5c > [ 77.337443] SOFTE: 1 > [ 77.337477] > GPR00: > [ 77.337517] c0000000005cefcc > [ 77.337575] c00000062b9a76d0 > [ 77.337626] c000000001103a00 > [ 77.337714] c00000063e058d40 > [ 77.337765] > GPR04: > [ 77.337817] c00000062b9a7740 > [ 77.337868] 0000000000000008 > [ 77.337927] 000000000005f000 > [ 77.337978] 000000063eed0000 > [ 77.338037] > GPR08: > [ 77.338080] c00000062f9629c8 > [ 77.338138] 0000000000000001 > [ 77.338191] fffffffffffff000 > [ 77.338248] c00000063e058e80 > [ 77.338300] > GPR12: > [ 77.338384] 0000000000000000 > [ 77.338435] c00000000fe00000 > [ 77.338498] 0000000020000000 > [ 77.338548] 0000000000000000 > [ 77.338605] > GPR16: > [ 77.338645] 0000000000000008 > [ 77.338703] 000000004d5906fc > [ 77.338754] 000000004d5a6c08 > [ 77.338811] 000000004d54b3d0 > [ 77.338866] > GPR20: > [ 77.338921] 000001000bcf8440 > [ 77.338972] 0000000000000000 > [ 77.339030] 0000000000000000 > [ 77.339080] c00000062523b078 > [ 77.339138] > GPR24: > [ 77.339178] c00000062523b080 > [ 77.339240] c000000000da2b58 > [ 77.339290] 0000000000000000 > [ 77.339347] c00000062e539600 > [ 77.339398] > GPR28: > [ 77.339485] 0000000000060000 > [ 77.339536] c00000062523b000 > [ 77.339594] c00000062e539600 > [ 77.339644] c00000062e539688 > > [ 77.339740] NIP [c0000000005cf018] .btrfs_qgroup_free_refroot+0x188/0x220 > [ 77.339852] LR [c0000000005ceff8] .btrfs_qgroup_free_refroot+0x168/0x220 > [ 77.339959] Call Trace: > [ 77.339998] [c00000062b9a76d0] [c0000000005cefcc] > .btrfs_qgroup_free_refroot+0x13c/0x220 > [ 77.340123] (unreliable) > [ 77.340193] [c00000062b9a7790] [c00000000054210c] > .commit_fs_roots+0x19c/0x240 > [ 77.340355] [c00000062b9a78a0] [c0000000005451a0] > .btrfs_commit_transaction.part.5+0x480/0xbe0 > [ 77.340554] [c00000062b9a7970] [c000000000503bd4] .btrfs_sync_fs+0x74/0x1c0 > [ 77.340725] [c00000062b9a7a10] [c0000000002d6ce0] > .sync_filesystem+0xd0/0x100 > [ 77.340891] [c00000062b9a7a90] [c000000000294f88] > .generic_shutdown_super+0x38/0x1a0 > [ 77.341052] [c00000062b9a7b10] [c000000000295508] > .kill_anon_super+0x18/0x30 > [ 77.342243] [c00000062b9a7b90] [c000000000503db8] > .btrfs_kill_super+0x18/0xd0 > [ 77.342411] [c00000062b9a7c10] [c0000000002958c8] > .deactivate_locked_super+0x98/0xe0 > [ 77.342573] [c00000062b9a7c90] [c0000000002be114] .cleanup_mnt+0x54/0xa0 > [ 77.342723] [c00000062b9a7d10] [c0000000000d7e74] > .task_work_run+0x124/0x180 > [ 77.342862] [c00000062b9a7db0] [c00000000001c354] > .do_notify_resume+0xa4/0xb0 > [ 77.343030] [c00000062b9a7e30] [c00000000000c344] > .ret_from_except_lite+0x70/0x74 > [ 77.343187] Instruction dump: > [ 77.343276] 3b400000 e87d0c78 38810070 4bffab1d 60000000 2c230000 4182ff40 > e8dfffc8 > [ 77.343522] eb630008 7d5c3010 7d294910 7d2900d0 <0b090000> 7fbc3040 > 41dd0070 f95fffc8 > [ 77.343771] ---[ end trace 8130fb71377d4ff8 ]--- > [ 77.343857] BTRFS warning (device loop1): qgroup 5 reserved space > underflow, have: 389120, to free: 393216 > [ 77.735193] BTRFS info (device loop1): disabling disk space caching > [ 77.736629] BTRFS info (device loop1): has skinny extents > > > The above call trace happens because of the following: > > |--------------------------------+-----------------------------------| > | Task A | Task B | > |--------------------------------+-----------------------------------| > | Write 4k bytes to a file | | > | at offset range [0, 4095] | | > | - __btrfs_buffered_write | | > | -- btrfs_check_data_free_space | | > | --- Set EXTENT_QGROUP_RESERVED | | > | bit for range [0, 64k-1] | | > | -- Copy 4k data from userspace | | > | to page cache | | > | | Write 4k bytes to the file | > | | at offset range [4096, 8191] | > | | - __btrfs_buffered_write | > | | -- btrfs_check_data_free_space | > | | --- Since EXTENT_QGROUP_RESERVED | > | | is already set we don't | > | | reserve qgroup space | > | | -- Assume the call to | > | | btrfs_delalloc_reserve_metadata() | > | | fails | > | | -- btrfs_free_reserved_data_space | > | | --- Clear EXTENT_QGROUP_RESERVED | > | | file range [4096, 8191] | > |--------------------------------+-----------------------------------| > > On x86_64, It has been almost impossible to get the call to > btrfs_delalloc_reserve_metadata() in __btrfs_buffered_write() to fail. Hence I > have the following change in __btrfs_buffered_write() ...
Setting a qgroup limit makes it fail pretty reliably. That's exactly
the test case I used when tracking down problem described in "[PATCH]
btrfs: Ensure proper sector alignment for btrfs_free_reserved_data_space"
I think this is also the same issue described there -- write_bytes can
be anything, but reserve_bytes is sector-aligned.
-Jeff
> if (pos != 2048)
> ret = btrfs_delalloc_reserve_metadata(inode, reserve_bytes);
>
>
> else
>
>
> ret = 1;
>
>
> if (ret) {
>
>
> if (!only_release_metadata)
>
>
> btrfs_free_reserved_data_space(inode, pos,
>
>
> write_bytes);
>
>
> else
> btrfs_end_write_no_snapshoting(root);
> break;
>
>
> }
>
>
> With the above change and by using max_inline=0 mount option, the following
> command line will reproduce the call trace on an x86_64 machine,
> $ xfs_io -f -c 'pwrite -b 2048 0 8192' -c sync /mnt/file-0.bin
>
--
Jeff Mahoney
SUSE Labs
signature.asc
Description: OpenPGP digital signature
